1. Field of the Invention
The present invention relates to a magnet holding member used in a rotating electrical machine, a rotor having the magnet holding member, a rotating electrical machine having the rotor, and a machine tool having the rotating electrical machine.
2. Description of the Related Art
A synchronous electric motor including a stator having a plurality of magnets is well known, in which the magnets are positioned on a surface of the rotor in the circumferential direction thereof. In such a synchronous electric motor, when the rotating speed of the rotor needs to be increased, it is necessary to increase the holding strength for the magnets on the stator, in order to prevent the magnets from being separated from the stator due to centrifugal force.
As a relevant prior art document, for example, JP H11-089142 A discloses a rotor of an electric motor, including a rotating shaft, a sleeve positioned on an outer surface of the rotating shaft, a permanent magnet having a cylindrical shape positioned on an outer surface of the sleeve, and a holding member made from carbon fiber reinforced plastic (CFRP), positioned on an outer surface of the permanent magnet.
In order to rotate the rotor at high speed, it is necessary that the holding member of the magnet have high strength. For example, when a holding member made from CFRP is used as described in JP H11-089142 A, the holding strength can be increased by increasing tension in the circumferential direction of the holding member. However, actually, a fiber of the holding member may be loosened when producing the holding member or an outer fiber layer may peel away from an inner fiber layer in the holding member. Therefore, it is difficult to increase the holding strength by increasing the tension.
The loosening of the fiber and/or the peeling of the fiber layer may occur, for example, when an FRP, formed by winding a sheet-like material on a cylindrical jig, is used as the holding member. Concretely, a terminal end and a vicinity portion of the wound sheet material cannot be sufficiently extended corresponding to the applied tension, and the outer layer may be separated from the inner layer, whereby the reliability of the rotor may be deteriorated. Such a problem is likely to occur in the terminal end of the wound sheet material. In addition, when large restoring force occurs in the holding member due to a large tightening margin of the holding member, the fiber of the outer layer may be loosened by entering between the fibers of the inner layer, whereby the required holding strength cannot be obtained.
Therefore, a reliable holding member is required, in which the start end and the terminal end of the wound sheet do not peel away, and the fiber of the outer layer does not enter between the fibers of the inner layer, even when the high holding strength of the holding member is required.